Primary and Secondary Metabolites in Lotus japonicus.

Lotus japonicus is a leguminous model plant used to gain insight into plant physiology, stress response, and especially symbiotic plant-microbe interactions, such as root nodule symbiosis or arbuscular mycorrhiza. Responses to changing environmental conditions, stress, microbes, or insect pests are generally accompanied by changes in primary and secondary metabolism to account for physiological needs or to produce defensive or signaling compounds. Here we provide an overview of the primary and secondary metabolites identified in L. japonicus to date. Identification of the metabolites is mainly based on mass spectral tags (MSTs) obtained by gas chromatography linked with tandem mass spectrometry (GC-MS/MS) or liquid chromatography-MS/MS (LC-MS/MS). These MSTs contain retention index and mass spectral information, which are compared to databases with MSTs of authentic standards. More than 600 metabolites are grouped into compound classes such as polyphenols, carbohydrates, organic acids and phosphates, lipids, amino acids, nitrogenous compounds, phytohormones, and additional defense compounds. Their physiological effects are briefly discussed, and the detection methods are explained. This review of the exisiting literature on L. japonicus metabolites provides a valuable basis for future metabolomics studies.

A High-Content Screen for the Identification of Plant Extracts with Insulin Secretion-Modulating Activity.

Bioactive plant compounds and extracts are of special interest for the development of pharmaceuticals. Here, we describe the screening of more than 1100 aqueous plant extracts and synthetic reference compounds for their ability to stimulate or inhibit insulin secretion. To quantify insulin secretion in living MIN6 ß cells, an insulin-Gaussia luciferase (Ins-GLuc) biosensor was used. Positive hits included extracts from Quillaja saponaria, Anagallis arvensis, Sapindus mukorossi, Gleditsia sinensis and Albizia julibrissin, which were identified as insulin secretion stimulators, whereas extracts of Acacia catechu, Myrtus communis, Actaea spicata L., Vaccinium vitis-idaea and Calendula officinalis were found to exhibit insulin secretion inhibitory properties. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) were used to characterize several bioactive compounds in the selected plant extracts, and these bioactives were retested for their insulin-modulating properties. Overall, we identified several plant extracts and some of their bioactive compounds that may be used to manipulate pancreatic insulin secretion.

Quantitative Determination of Thiamine-Derived Taste Enhancers in Aqueous Model Systems, Natural Deep Eutectic Solvents, and Thermally Processed Foods.

To obtain high-kokumi-active building blocks, which can be used to produce savory process flavors, it is essential to obtain a better understanding on the formation rate of kokumi-active compounds, such as 3-(((4-amino-2-methylpyrimidin-5-yl)methyl)thio)-5-hydroxypentan-2-one or 2-methyl-5-(((2-methylfuran-3-yl)thio)methyl)pyrimidin-4-amine. The present work showed quantitative studies in several model reaction systems on the recently discovered kokumi-active thiamine derivates. It was possible to show that the thiamine conversion in aqueous model reactions could be directed toward the taste-modulating compounds by adjusting the pH value (6.5), the heating time (120 min), and the heating temperature (120 °C). With the development of a new natural deep eutectic solvents (NADES) system consisting of thiamine, cysteine, ribose, and sodium hydroxide, it was possible to obtain high yields of the targeted taste-modulating analytes, such as 3-(((4-amino-2-methylpyrimidin-5-yl)methyl)thio)-5-hydroxypentan-2-one and 2-methyl-5-(((2-methylfuran-3-yl)thio)methyl)pyrimidin-4-amine. Furthermore, the current study showed that kokumi-active thiamine derivates, such as S-((4-amino-2-methylpyrimidin-5-yl)methyl)-l-cysteine, 3-(((4-amino-2-methylpyrimidin-5-yl)methyl)thio)-5-hydroxypentan-2-one, 2-methyl-5-(((2-methylfuran-3-yl)thio)methyl)pyrimidin-4-amine, and 5-(((furan-2-ylmethyl)thio)methyl)-2-methylpyrimidin-4-amine, can be classified as natural "food-borne" taste enhancers and occur in thiamine-rich, thermally treated foodstuff.

Novel Taste-Enhancing 4-Amino-2-methyl-5-heteroalkypyrimidines Formed from Thiamine by Maillard-Type Reactions.

Increasing the thiamine concentration in a respective process flavor yields a product with a significant higher kokumi activity. S-plot analysis of the mass spectrometric data revealed beside thiamine itself, 4-methyl-5-thiazoleethanol, (S)-((4-amino-2-methylpyrimidin-5-yl)methyl)-l-cysteine, N-((4-amino-2-methylpyrimidin-5-yl)methyl)formamide, 3-(((4-amino-2-methylpyrimidin-5-yl)methyl)thio)-5-hydroxypentan-2-one, and 2-methyl-5-(((2-methylfuran-3-yl)thio)methyl)pyrimidin-4-amine as marker molecules for a process flavor with higher thiamine concentration. Sensory-based targeted isolation revealed that (S)-((4-amino-2-methylpyrimidin-5-yl)methyl)-l-cysteine, 3-(((4-amino-2-methylpyrimidin-5-yl)methyl)thio)-5-hydroxypentan-2-one, and 2-methyl-5-(((2-methylfuran-3-yl)thio)methyl)pyrimidin-4-amine showed an influence on the kokumi taste activity with taste threshold concentrations between 35 and 120 µmol/L. An adapted mass spectrometric-based carbon module labeling experiment as well as quantitative studies clearly demonstrated thiamine as the only precursor and an intermolecular formation pathway for the compounds (S)-(((4-amino-2-methylpyrimidin-5-yl)methyl)thio)-5-hydroxypentan-2-one and 2-methyl-5-(((2-methylfuran-3-yl)thio)methyl)pyrimidin-4-amine. On the basis of the knowledge that several thiamine derivatives showed taste-modulating activity, selected thiamine-based binary model reactions and synthesis were carried out. This resulted in the isolation of further thiamine-derived taste modulators like (S)-((4-amino-2-methylpyrimidin-5-yl)methyl)-l-cysteinylglycine, (S)-3-((((4-amino-2-methylpyrimidin-5-yl)methyl)thio)methyl)piperazine-2,5-dione, 3-(((4-amino-2-methylpyrimidin-5-yl)methyl)thio)pentan-2-one, 5-(((furan-2-ylmethyl)thio)methyl)-2-methylpyrimidin-4-amine, and (4-amino-2-methylpyrimidin-5-yl)methanethiol, 2-methyl-5-((methylthio)methyl)pyrimidin-4-amine with taste thresholds ranging from 35 to 880 µmol/L.

Construction and Application of a Database for a Five-Dimensional Identification of Natural Compounds in Garcinia Species by Means of UPLC-ESI-TWIMS-TOF-MS: Introducing Gas Phase Polyphenol Conformer Drift Time Distribution Intensity Ratios.

Thirty-four reference compounds from G. buchananii were analyzed by means of UPLC-ESI-IMS-TOF-MS to build a database consisting of retention time, accurate m/ z of precursors and fragment ions, and rotationally averaged collision cross-sectional area (CCS). The CCS value of six selected compounds analyzed in bark extract in different concentrations and solvent systems showed excellent intra- and interday precision (RSD ≤ 0.9%). The established database was applied on different organs of G. buchananii as well as G. kola, G. mangostana, and G. cambogia enabling a fast and reliable identification of these natural bioactives. For several compounds, more than one drift time species could be highlighted, which we propose to be hydrogen bond stabilized rotational isomers transferred from solution to gas phase. We used all CCS values of one compound, and we propose to add also the intensity ratio of the conformers as a new and additional characteristic compound parameter in compound identification/screening/database applications to reduce dereplication and false positives and to strengthen the identification.